Radar apparatus using a pulse signal radiate radio waves to the space on the basis of a pulse signal to be transmitted, receive a pulse signal of reflection waves reflected from a target, and measure at least one of a distance between a measuring site and the target and a direction of the target. In recent years, radar apparatus which can detect targets including automobiles and pedestrians by performing a high-resolution measurement using short-wavelength radio waves including microwaves and millimeter waves have been being developed.
For example, Patent document 1 is known as disclosing a radar apparatus which suppresses interference by reducing measurement times of respective sector radars. The radar apparatus disclosed in Patent document 1 will be outlined with reference to FIG. 23. FIG. 23 is an explanatory diagram (timing chart) for description of how the conventional radar apparatus operates.
The radar apparatus of Patent document 1 is equipped with two radar devices, that is, an A radar device and a B radar device. The A radar device is equipped with a sync unit for controlling the timing of an A pulse signal to be transmitted from the A radar device and an I/F unit for receiving a B sync trigger signal that is synchronized with a B pulse signal transmitted from the B radar device. The A radar device receives the B trigger signal from the B radar device through the I/F unit. The A radar device controls the emission timing of the A pulse signal to be emitted from the A radar device on the basis of the received B sync signal.
Therefore, as shown in FIG. 23, the arrival time of an interference wave signal that the B radar device receives from the A radar device always exists in a time interval Tx that is outside an effective reception period of the B radar device. The interference signal that the B radar device receives from the A radar device does not affect a measurement of the B radar device.
The arrival time of an interference wave signal that the A radar device receives from the B radar device exists in an effective reception period of the A radar device. However, the A radar device can eliminate an interference signal effectively by performing restrictive interference suppression processing or gate processing on the interference wave signal coming from the B radar device. In FIG. 23, parameter Tm represents the effective reception period, parameter Tx represents the time interval between effective reception periods, parameter Td represents a time that elapses to arrival of interference waves from the other radar device.
For example, Patent document 2 is known as disclosing a radar apparatus which suppresses occurrence of interference even if reflection signals reflected from a target are received in an asynchronous manner, by using complementary codes (P1, P2) and (Q1, Q2) which are complete complementary codes.
Two radar systems of Patent document 2 transmit and receive different coded pulses (P1, P2, Q1, Q2) as coded pulses of a complete complementary code using carrier waves in the same frequency band.
When receiving plural coded pulses transmitted from the self radar system, one radar system outputs one of autocorrelation function signals RP1P1(τ), RP2P2(τ), RQ1Q1(τ), and RQ2Q2(τ) corresponding to the plural respective coded pulses (P1, P2, Q1, Q2). When receiving plural coded pulses transmitted from the other radar system, the one radar system outputs one of cross-correlation function signals RQ1P1(τ), RQ2P2(τ), RP1Q1(τ), and RP2Q2(τ) corresponding to the plural coded pulses (P1, P2) or (Q1, Q2).
Because of the properties of the complete complementary code, the sum of plural outputs autocorrelation function signals (RP1P1(τ)+RP2P2(τ) or RQ1Q1(τ)+RQ2Q2(τ)) is equal to 0 except for τ being equal to 0 and the sum of plural outputs cross-correlation function signals (RQ1P1(τ)+RQ2P2(τ) or RP1Q1(τ)+RP2Q2(τ)) is equal to 0 irrespective of τ.
The reception side performs reception processing of calculating plural autocorrelation function signals corresponding to plural respective coded pulses (P1, P2, Q1, Q2) transmitted from the self radar system. As a result, compressed pulses that are free of sidelobes are obtained. Even when plural coded pulses transmitted from the other radar system are received, signal components of the other radar system can be made zero in a process of calculating the sum of autocorrelation function signals. That is, plural radar systems that do not interfere with each other can be provided even if the same frequency band is used between adjoining frequency bands.